All epithelia rest on a basement membrane. The basement membrane provides structural support and integrity to epithelia by providing a common framework of proteins to which epithelial cells adhere. The basement membrane separates the epithelia from the underlying or surrounding tissue. Importantly, because epithelia lack blood vessels and depend upon capillaries in surrounding tissues, all nutrients, hormones and other proteins must diffuse across the basement membrane before reaching an epithelia.
Epithelial cells interact with the basement membrane via receptors in their cell membrane called integrins. Systems Cell Biology Yale Epithelia Lab Learning Objectives Distinguish between, simple, stratified, and pseudostratified epithelia List characteristics of squamous, cuboidal, and columnar epithelia Identify some common surface specializations of epithelia. Lab Content Introduction Epithelia are tissues composed of closely aggregated cells that cover most body surfaces, cavities, and tubes.
Simple squamous epithelium Simple squamous epithelia consist of a single layer of flattened cells. Simple cuboidal epithelium Simple cuboidal epithelium consist of a single layer of cells that are approximately as tall as they are wide. Simple columnar epithelium Simple columnar epithelium consist of a single layer of cells that are taller than they are wide.
Stratified Squamous Epithelium Stratified squamous epithelia consist of multiple layers of cells with the outer most layer being squamous.
Simple epithelium consists of a single layer of cells. They are typically where absorption, secretion and filtration occur. The thinness of the epithelial barrier facilitates these processes.
Simple epithelial tissues are generally classified by the shape of their cells. The four major classes of simple epithelium are: 1 simple squamous; 2 simple cuboidal; 3 simple columnar; and 4 pseudostratified. Simple squamous epithelium cells are flat in shape and arranged in a single layer. This single layer is thin enough to form a membrane that compounds can move through via passive diffusion.
This epithelial type is found in the walls of capillaries, linings of the pericardium, and the linings of the alveoli of the lungs. Simple cuboidal epithelium consists of a single layer cells that are as tall as they are wide. The important functions of the simple cuboidal epithelium are secretion and absorption. This epithelial type is found in the small collecting ducts of the kidneys, pancreas, and salivary glands.
Simple columnar epithelium is a single row of tall, closely packed cells, aligned in a row. These cells are found in areas with high secretory function such as the wall of the stomach , or absorptive areas as in small intestine. They possess cellular extensions e. These are simple columnar epithelial cells whose nuclei appear at different heights, giving the misleading hence pseudo impression that the epithelium is stratified when the cells are viewed in cross section.
Overview and Key Difference 2. What is Simple Squamous 3. What is Simple Cuboidal 4. Simple squamous epithelial tissue is composed of a single layer of flat polygonal or hexagonal shaped cells.
Each cell has a centrally located, spherical nucleus and irregular boundaries. Also, its main functions are protection, filtration, absorption and secretion. Simple cuboidal tissue is composed of a single layer of cuboidal shaped cells with the same height and width. Furthermore, this tissue is distributed in the ducts and glands, which include pancreatic ducts and salivary glands. It is also distributed along the renal tubule.
The mesothelium is a simple squamous epithelium that forms the surface layer of the serous membrane that lines body cavities and internal organs. Its primary function is to provide a smooth and protective surface.
Mesothelial cells are squamous epithelial cells that secrete a fluid that lubricates the mesothelium. In simple cuboidal epithelium , the nucleus of the box-like cells appears round and is generally located near the center of the cell.
These epithelia are active in the secretion and absorptions of molecules. Simple cuboidal epithelia are observed in the lining of the kidney tubules and in the ducts of glands.
In simple columnar epithelium , the nucleus of the tall column-like cells tends to be elongated and located in the basal end of the cells. Like the cuboidal epithelia, this epithelium is active in the absorption and secretion of molecules. Simple columnar epithelium forms the lining of some sections of the digestive system and parts of the female reproductive tract. Ciliated columnar epithelium is composed of simple columnar epithelial cells with cilia on their apical surfaces.
These epithelial cells are found in the lining of the fallopian tubes and parts of the respiratory system, where the beating of the cilia helps remove particulate matter. Pseudostratified columnar epithelium is a type of epithelium that appears to be stratified but instead consists of a single layer of irregularly shaped and differently sized columnar cells. In pseudostratified epithelium, nuclei of neighboring cells appear at different levels rather than clustered in the basal end.
The arrangement gives the appearance of stratification; but in fact all the cells are in contact with the basal lamina, although some do not reach the apical surface. Pseudostratified columnar epithelium is found in the respiratory tract, where some of these cells have cilia.
Both simple and pseudostratified columnar epithelia are heterogeneous epithelia because they include additional types of cells interspersed among the epithelial cells.
A stratified epithelium consists of several stacked layers of cells. This epithelium protects against physical and chemical wear and tear. The stratified epithelium is named by the shape of the most apical layer of cells, closest to the free space. Stratified squamous epithelium is the most common type of stratified epithelium in the human body.
The apical cells are squamous, whereas the basal layer contains either columnar or cuboidal cells. The top layer may be covered with dead cells filled with keratin. Mammalian skin is an example of this dry, keratinized , stratified squamous epithelium.
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